A printing ink for the printing of security documents by the method of engraved steel die printing, having a viscosity of at least 1 Pa.multidot.s at 40.degree. C. under a shear of about 1000 sec.sup.-1, containing a binder matrix, a polymerization initiator for polymerizable matrix components, fillers and pigments, and the usual additives. The binder matrix contains at least one cationically polymerizable compound, modified to bring about the desired rheology of the ink, and the photoinitiator, activable by UV, heat and EB, is an onium salt capable of releasing a Lewis or Bronsted acid.This ink has best and very rapid drying characteristics.